In an alternate history New York City—one hundred and fifty years after an earthquake from hell nearly destroyed the planet—the twenty-first century clings to an industrial age. Steam engines rule, and demon-powered technology is the up and coming thing. Henry Paine, a half-demon taxi driver, is the go-to guy for just the right demon to possess your machine and automate any mechanical gizmo with or without an engine. The creatures are tame as pets. Or at least they have been… until now.
Wanda Snow is an exorcist who grudgingly admits to having a few drops of demon blood herself. She's come to New York to rid the city of demonic vermin as well as any other demons that get in her way. Wanda and Henry are naturally at odds, but the two are forced to become partners in a mutual goal to round up the rogue demons biting the Big Apple.
A third of the U.S. is populated by Hellspawn: half-breed demons, like Henry. A rebellion has been brewing for decades, and Henry's former best friend Jasper is leader of a gang known as The Demon Lords. Jasper, like all Hellspawn, outlived his abusive human family, and he despises the human race. Starting with NYC, his goal is to wipe out the humans and make Hellspawn the dominating race that will someday rule the world.
Henry and Wanda must use their psychic gifts to fight Jasper and foil his plans, but there's a lot working against them: insane cultists, ghost sickness, rogue machines, hungry demon minions... Their list of adversaries grows daily, and preventing themselves from becoming each other's enemy is a constant challenge that almost undoes them both.